Abstract: New penicillin esters and their salts together with methods for, and intermediates in the preparation thereof, the esters having the formula: ##EQU1## in which formula the asterisk indicates the possibility of an asymmetric carbon atom, n indicates an integer from 0 to 5, R.sup.1 represents a group, which together with --CO-- forms the side chain of any of the known semisynthetic, biosynthetic, and natural penicillins; R.sup.2 has any of the following meanings: hydrogen, an aliphatic, an aromatic, a heterocyclic group, and an aromatically substituted aliphatic group; each of R.sup.3, R.sup.4, and R.sup.5 represents hydrogen, or a lower aliphatic group with the provision that R.sup.2 and R.sup.5 together with the carbon atom between them can form a 5-, 6-, or 7-membered carbocyclic ring, and either R.sup.3 and R.sup.4, or R.sup.4 and R.sup.5 together with the nitrogen atom can form a ring system.